Laser surgery has become a generally useful technique, requiring specialized equipment and techniques. Laser surgery is indicated in the treatment of many eye diseases. For example, lasers are used to treat the ocular complications of diabetes. For glaucoma patients, lasers help to control the pressure inside the eye when medications alone do not succeed. Lasers are used to seal holes in the retina, and prevent or treat retinal detachments. Macular degeneration is another condition where lasers can sometimes help prevent vision loss. Laser surgery is also used after cataract surgery to improve vision, if necessary.
The retinal pigment epithelium (RPE) is a single cell layer, situated in the back of the eye behind a sensitive neuroretinal layer, with a high pigment density that can be targeted by laser irradiation. Retinal laser surgery can be classified into techniques which rely on thermal damage to the neuroretinal layer (such as retinal welding), and those that desirably do not involve damage to the neuroretinal layer (such as photocoagulative treatment of central serous retinopathy, diabetic macular edema, and drusen).
Conventional laser photocoagulation of the retina is performed with long pulses (on the order of from about 10 to about 500 ms) generated from a continuous wave laser, with the majority of the energy absorbed by the RPE. Heat diffusion during the long exposure to the laser pulse results in a relatively large zone of thermal damage, causing irreversible thermally-induced damage of not only the RPE cells, but also the photoreceptors and the choroicapillaris, producing scotomas (blind spots) in the treated areas.
Selective RPE photocoagulation is a recently developed therapeutic approach that uses short (microsecond) laser pulses to, ideally, target retinal pigment epithelial cells while not affecting adjacent photoreceptors in the retina, as described in U.S. Pat. No. 5,302,259 to Birngruber, and U.S. Pat. No. 5,549,596 to Latina. These treatment methods do not produce blind spots, as does conventional laser photocoagulation. In fact, this treatment does not produce any visible changes in the fundus during treatment. However, clinicians have to rely on post surgery fluorescein angiography to determine if the treatment endpoint has been reached, a treatment that requires approximately an hour and is inconvenient for the patient.